add synthetic id in window object

[wjlei1990]

Hi Lion,

I found it sometimes useful to add synthetic trace id in window object. Currently, only the observed id is stored in the window object as channel_id. But quite often, when we use window selection results, we need bot refer to observed and synthetic id.

If we are going to store the synthetic name, what should be the attribute name of it? synt_channel_id?

Let me know what do you think?